Communication devices within a wireless communications network may be e.g., stations (STAs), User Equipments (UEs), mobile terminals, wireless terminals, terminals, and/or Mobile Stations (MS). Wireless devices are enabled to communicate wirelessly in a cellular communications network or wireless communication network, sometimes also referred to as a cellular radio system, cellular system, or cellular network. The communication may be performed e.g., between two wireless devices, between a wireless device and a regular telephone, and/or between a wireless device and a server via a Radio Access Network (RAN), and possibly one or more core networks, comprised within the wireless communications network. Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, or tablets with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the Radio Access Network (RAN), with another entity, such as another terminal or a server.
Communication devices may also be network nodes, or Transmission Points (TP). The wireless communications network covers a geographical area which may be divided into cell areas, each cell area being served by an access node such as a Base Station (BS), e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g., evolved Node B (“eNB”), “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g., Wide Area Base Stations, Medium Range Base Stations, Local Area Base Stations and Home Base Stations, based on transmission power and thereby also cell size. A cell may be understood as the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The wireless communications network may also be a non-cellular system, comprising network nodes which may serve receiving nodes, such as wireless devices, with serving beams. In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks. In the context of this disclosure, the expression Downlink (DL) may be used for the transmission path from the base station to the wireless device. The expression Uplink (UL) may be used for the transmission path in the opposite direction i.e., from the wireless device to the base station. 3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
The standardization organization 3GPP is currently in the process of specifying a New Radio Interface called NR or 5G-UTRA, as well as a Fifth Generation (5G) Packet Core Network, which may be referred to as Next Generation Core Network, abbreviated as NG-CN, New Generation Core (NGC) or 5G CN. The current understanding of various concepts related to this work may be based on input from 3GPP TS 23.799 v1.1.0, and it is summarized below.
Initial High Level Architectural View
FIG. 1 is a schematic representation of the current high level architecture of a system according to the Next Generation, also referred to as a Next Gen System. This high level architecture may be used as a reference model herein. FIG. 1 shows the NextGen UE, NextGen®AN, NextGen Core and their reference points.
If, and possibly how, the NextGen UE may interface with the NextGen Core is currently set for further study.
Reference points in the Next Gen System may be as follows:
NG2: Reference point for the control plane between NextGen®AN and NextGen Core.
NG3: Reference point for the user plane between NextGen®AN and NextGen Core.
NG1: Reference point for the control plane between NextGen UE and NextGen Core.
NG6: It is the reference point between the NextGen Core and the data network. The data network may be an operator external public or private data network or an intra-operator data network, e.g., for provision of IP Multimedia Services (IMS) services. This reference point corresponds to SGi for 3GPP accesses.
The 5G RAN may comprise base stations supporting evolved LTE and/or New Radio (NR) radio access. The term for a 5G/NR eNB is gNB, i.e., the new 5G/NR base station is referred to as a gNB.
The 5G System is expected to support deployments in virtualized environments and introduce support for scaling of a network function instance; and dynamic addition or removal of a network function instance.
The 5G system currently being standardized by 3GPP is expected to often be deployed in conditions where achieving appropriate coverage, e.g., cell edge coverage, may be challenging. This may be especially the case when high carrier frequencies, e.g., >6 Giga Hertz (GHz) may be utilized.
To combat the low Signal-to-Noise Ratio (SNR)/Signal to Interference plus Noise Ratio (SINR), a UE may experience at the coverage edge, as well as to achieve high data rates, beamforming, where the radiated energy may be focused in a more or less narrow beam, is expected to be commonly used. In deployments with high carrier frequencies, both dedicated data transmission and common control channel transmissions may be subject to beamforming. In the latter case in particular, the purpose is to achieve acceptable SNR/SINR at the edge of the coverage area. In deployments with lower or semi-high carrier frequencies, common control channels may be transmitted using omnidirectional transmission or wide beam, e.g., sector coverage, transmission, possibly with some repetition, while narrow high-gain beamforming may still be used for dedicated communication, where a single specific UE is targeted, in order to achieve high data rates, especially for user plane communication.
In addition to the Radio Resource Control (RRC)_IDLE and RRC_CONNECTED states of LTE, a new state is introduced in NR, tentatively denoted RRC_INACTIVE, which may be understood to be similar to the new Suspended mode, which is currently being specified for LTE. In this state, the UE context, that is, the information associated with the UE, such as security parameters and bearer configuration information, in the RAN, that is, in a gNB, and the S1 connection, that is, the UE associated connection between the RAN and the core network, assumedly between a gNB in the RAN and a Mobility Management Entity (MME) in the NGC, may be maintained, but no radio bearers are kept active. The UE context and S1 connection may be maintained by a gNB that may be referred to as “anchor gNB”, typically the gNB with which the UE was last in RRC_CONNECTED state. A UE in RRC_INACTIVE state may move around in a limited area, e.g., called “RAN based notification area” without notifying the network. If the network needs to reach the UE for DL data transmission, it may page—or notify—the UE in the RAN based notification area allocated to the UE, possibly in a stepwise approach, where the UE may be first paged/notified in a smaller area, which may be stepwise increased in case the UE does not respond to the page/notification. If the UE leaves its RAN based notification area, it may notify the network, which may allocate a new RAN based notification area to the UE, and may also move the UE context and S1 connection, visible to the core network as a path switch to the gNB, where the UE notified its presence.
For a UE in RRC_IDLE state, the RAN may maintain no context and no S1 connection, but the core network may maintain state information and keep track of the whereabouts of a UE on a coarse level, defined by a list of Tracking Areas configured for the UE. A UE in RRC_IDLE state may move around without notifying the network within the cells covered by the list of Tracking Areas allocated to the UE by the core network, e.g. by a MME. If the UE enters a cell which is not covered by the list of Tracking Areas of the UE, it may notify the network through a Tracking Area Update procedure.
A UE in RRC_IDLE or RRC_INACTIVE state may monitor the appropriate control channel for paging in the cell the UE may be currently located in. To determine the appropriate cell for monitoring for paging, the UE may perform measurements on the appropriate DL signals in available cells, and may select the most suitable cell in accordance with the measurement results, typically, the cell where the UE experiences the best DL radio channel quality, e.g. in terms of SNR or SINR. The DL signals to measure on for this purpose may be reference signals, such as Cell Specific Reference signals (CSR) in LTE or, in NR, synchronization signals, serving as reference signals too, i.e., Primary Synchronization Signals (PSS), Secondary Synchronization Signals (SSS), a.k.a., NR-PSS, NR-SSS, and possibly Tertiary Synchronization Signals (TSS), or possibly Synchronization Signals (SS) Block transmissions and/or possibly separate reference signals. The SS Block in NR may consist of synchronization signal components, PSS, SSS and possibly TSS1, combined with a broadcast channel denoted NR Physical Broadcast Channel (NR-PBCH). A UE that keeps track of the synchronization and monitors for paging in a selected cell is said to be camping on that cell. The UE may also have to acquire, at least relevant parts of, the system information in the cell it may be camping on.
A UE in RRC_IDLE or RRC_INACTIVE state camping on a cell may spend most of its time in an energy saving low-power mode, often referred to as Discontinuous Reception (DRX) sleep mode. It may wake up only to reacquire synchronization, monitor the DL for pages, at configured paging occasions, and to perform channel quality measurements in the current cell and possibly neighbor cells, for the purpose of cell reselection assessment, that is, to assess whether it should start camping on another cell. Typically, the UE may reacquire synchronization, if needed, and perform channel quality measurements in conjunction with the page monitoring. In addition, the UE may occasionally acquire the relevant system information in the current and/or neighboring cells.
As mentioned above, the UE may perform cell reselection assessments and decisions based on radio channel quality measurements in the current and neighbor cells. In addition, the UE may have to take into account channel quality thresholds and cell specific offsets, which the network may optionally configure and convey to the UE in the form of system information in the current/serving cell, and which may govern which differences in radio channel quality between the current and a certain neighbor cell may trigger cell reselection to the concerned neighbor cell. If the radio channel quality measurements motivate a cell reselection, then the UE may have to acquire relevant parts of the system information in the candidate cell, that is, the neighbor cell that may be being considered for cell reselection, to check that there are no obstacles for the UE to camp on it, e.g., that the cell is not barred, or is a Closed Subscriber Group (CSG) cell that is closed for the UE, or belongs to an area where the UE is not allowed service, or to a Public Land Mobile Network (PLMN) the UE is not allowed to access, before actually executing the cell reselection.
Existing methods for cell reselection assessments and decisions based on radio channel quality measurements in current and neighbor cells in deployments such as 5G/NR deployments may result in suboptimal choice of cell for reselection, creation of unnecessary overhead, and may result in ping-pong behavior by the UE.